The present invention relates to a wireless communication method and a wireless communication apparatus, or in particular a technique for realizing the cellular communication with the orthogonal frequency division multiple access (OFDMA) by employing the orthogonal frequency division multiplexing (OFDM).
In the wireless communication, the number of frequency resources available for use is limited, and therefore, a key playing a great role in realizing a system is how to achieve a high frequency utilization efficiency and a high communication speed. With this as a background, the research and development are under way for the wireless communication technique employing OFDM making possible the user scheduling even in frequency domain. In OFDM, the data to be transmitted is generated in frequency domain, and converted into a signal in time domain by IFFT (inverse fast Fourier transform) and transmitted as a wireless signal. At the receiving end, the signal in time domain is converted into a signal in frequency domain by FFT (fast Fourier transform) and the original signal is retrieved. In conducting the communication, control channels such as an access channel for establishing a link for the up link, a wireless control channel for transmitting the control information of the down link and up link and a broadcast channel for notifying the information on channel allotment and the system are required in addition to the data channel for data transmission.
The standardization organization IEEE802.20 has proposed a wireless scheme based on OFDM, and according to IEEE C802.20-06/04, the down link wireless control channel for transmitting the control information for the down link is defined. Also, the standardization organization 3GPP proposes a wireless scheme based on OFDM as LTE (long term evolution), and according to 3GPP TR 25.814 V7.0.0 (2006-06), the down link wireless control channel described above is defined. Further, the standardization organization 3GPP2 proposes a wireless scheme based on OFDM as LBC (loosely backward compatible), and according to 3GPP2 C30-20060620-054R2, the down link wireless control channel for transmitting the down link control information is defined.
The wireless control channel for the wireless communication schemes including and before the code division multiple access (CDMA) is always separated into the data channel and the control channel by time division, frequency division or code division. In the CDMA communication scheme, for example, a plurality of channels are transmitted at the same time by a diffused code, and at the receiving end, the required information can be retrieved by the inverse diffusion operation using a specified code. In this scheme, the diffused code allotted to the control channel is predetermined.
In the third-generation mobile communication now under development, on the other hand, the trend has changed toward the communication in which all information are carried on IP. In keeping with this trend, the broadband system has become a common practice and various forms of information are required to be exchanged in the next-generation communication utilizing OFDM. Some examples of the various forms of information are the data communication of best-effort type, the audio communication such as VoIP and the video streaming information.
In order to realize a broader band system, a method of the next-generation communication is proposed in which without any line dedicated to the wireless control channel, a part of the channel made up of OFDM is used for the wireless control channel as well as for the normal data channel. In accordance with the number of wireless mobile stations connected, the number of wireless channels required by each mobile station and the situation of the propagation path, the resource allotment to the wireless control channel is adaptively controlled. In this way, the overhead due to the wireless control channel that has thus far been caused by the margin design can be reduced.
IEEE C802.20-06/04 describes a method in which the wireless control channel such as the down link control channel F-SSCH is transmitted using several channels configured of OFDM. In this wireless control channel, the allotted amount and arrangement are declared at the head of the superframe.
The mobile station connected to the base station using this method in which the allotted amount and arrangement of the wireless control channel are declared at the head of the superframe receives the wireless control channel in the following steps:
Step 101: The information on the allotment of the control channel described in the preamble at the head of the superframe is acquired. The superframe is a unit configured of several PHY frames and a preamble is transmitted at the head thereof.
Step 102: The corresponding PHY frame is retrieved from the received signal and the wireless control channel is demodulated according to a predetermined demodulation method.
3GPP2 C30-20060626-054R2 describes a method similar to IEEE C802.20-06/04, in which the power is controlled for the down link wireless control channel and the resources of the transmission power as well as the product of time and frequency are optimized thereby to reduce the interference with other cells.
The PHY frame described above is the unit of minimum division in the direction of time in wireless area configured of a plurality of OFDM symbols. The process of channel coding is executed in this PHY frame unit.
FIG. 1 is a diagram showing the frame structure of 3GPP2 C30-20060626-054R2.
In FIG. 1 showing the superframe structure for TDD, a preamble is arranged at the head of the superframe.
FIG. 2 shows the preamble structure. The preamble has the structure shown in FIG. 2, and includes a pilot field (TDM1, TDM2, TDM3) for frame synchronization by the terminal and the broadcast information (pBCH0, pBCH1). The “PHY frame” is differently called according to a different standardization and may be referred to as a subframe.